Metal Clad Fiber Optics for Enhanced Heat Dissipation

ABSTRACT

An integrated optical I/O and semiconductor chip with a direct liquid jet impingement cooling assembly are disclosed. Contrary to other solutions for packaging an optical I/O with a semiconductor die, this assembly makes use of a metal clad fiber, e.g. copper, which will actually enhance cooling performance rather than create a design restriction that has the potential to limit cooling capability.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/550,842, filed Oct. 19, 2006, entitled “Metal Clad Fiber Optics ForEnhanced Heat Dissipation”, the contents of which are incorporated byreference herein in their entirety. U.S. patent applications Ser. No.11/427,380, filed Jun. 29, 2006, entitled “Direct Liquid Jet ImpingementModule for High Heat Flux Electronics Packages”; and Ser. No.10/904,555, filed Nov. 16, 2004, entitled “Fluidic Cooling Systems andMethods For Electronic Components”, are assigned to the same assigneehereof, International Business Machines Corporation of Armonk, N.Y., andcontain subject matter related, in certain respect, to the subjectmatter of the present application. The above-identified patentapplications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention pertains to cooling semiconductor chips. In particular,this invention utilizes heretofore unused thermal channels, therebyproviding enhanced heat dissipation for electronic products.

2. Description of the Prior Art

Many advanced microprocessor designs are reaching the limits of thermaldissipation which can be accommodated by air cooling alone. Examplesinclude multi-core processors, multi-chip modules, as well as highperformance microprocessors used for home entertainment. Efforts tocontrol thermal dissipation through redesign of the chips have met withsome success, but the use of air cooling places fundamental limitationson the thermal management of these systems. In addition, many of thesechips require very high I/O count and high interconnect density, whichhas begun to push the limits of conventional electrical interconnects.In order to address both of these concerns, we propose a version ofdirect liquid jet cooling for these applications which incorporatesmetal clad optical fibers to enhance cooling performance. Metal cladfibers have been recommended in the technical literature for highlycorrosive environments and for increased mechanical protection of theglass fiber but have never been designed into a microprocessor packageto provide cooling enhancing properties.

SUMMARY OF THE INVENTION

The use of metal-clad glass fibers in a direct liquid jet coolingpackage is novel. We have determined that it is possible to design metalclad optical fiber I/O which does not compromise the integrity of theseal frame surrounding a microprocessor or other electronic device thatis cooled by the use of a direct liquid jet impingement (“DLJI”) module.We have calculated the effect of typical metal-clad fibers on a directimpingement cooling system, and have shown there is a demonstrableeffect from using this feature. Furthermore, the use of fiber optic I/Orequires optical transmitters, for example, semiconductor verticalcavity surface emitting lasers (“VCSELs”), and photodetectors to beembedded in the microprocessor or other electronic device. Both of thesecomponents add thermal loading to the system, in particular the VCSELscan add a significant amount of heat.

Thus, there is a need for the cooling enhancements afforded by the metalclad fibers in this application. It may not be practical to incorporateoptical I/O without the benefit of this cooling. This design haspotential to be incorporated into commercial product offerings from IBMand other companies since other companies are also exploring thefeasibility of liquid cooling in future designs.

An integrated optical I/O and semiconductor chip with a DLJI coolingassembly are disclosed. Contrary to other solutions for packaging anoptical I/O with a semiconductor die, this assembly makes use of a metalclad fiber, e.g. copper, which will actually enhance cooling performancerather than create a design restriction that has the potential to limitcooling capability.

These, and other, aspects and objects of the present invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingpreferred embodiments of the present invention and numerous specificdetails thereof, is given by way of illustration and not of limitation.Many changes and modifications may be made within the scope of thepresent invention without departing from the spirit thereof, and theinvention includes all such modifications. The figures below are notintended to be drawn to any accurate scale with respect to size, shape,angular relationship, spatial relationship, or relative positions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a typical layout of a printed circuit board,semiconductor substrate, or similar multi-chip module assembly.

FIG. 2 illustrates a detailed cross section of an optical fiber having ametallic cladding.

FIG. 3 illustrates a design for the direct liquid jet impingementcooling module.

FIG. 4 illustrates a generalized side cross section view of the coolingfluid flow of the present invention.

FIG. 5 illustrates an exploded view of the direct liquid jet impingementcooling module and an example layout of the printed circuit board shownin FIG. 1.

FIG. 6 illustrates a cross section view of the direct liquid jetimpingement cooling module and an expanded view of the sealing meniscus.

FIG. 7 illustrates a thermally conductive epoxy or solder coupling ametal clad fiber to a semiconductor die.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a typical layout of a printed circuit board, semiconductormultiple chip module, or similar substrate assembly. In this examplethere is illustrated a microprocessor 105 as an example semiconductormain processor chip, decoupling capacitors 104, which could alternatelybe additional discrete semiconductor devices including multipleprocessors, or processor units, or memory chips, and fiber optic I/Oconnector 101. A ribbon of metal clad optical fibers 102 runs from themicroprocessor 105 to the edge of the substrate 103, where it terminatesin the optical connector 101. Wiring within substrate 103 provideselectrical communication coupling between the devices mounted thereon.The metal clad fibers 103 are flexed near their point of contact withmicroprocessor 105 to provide strain relief and facilitate attachment tothe microprocessor. The flex point can be placed at other points alongthe fibers or mechanical strain relief devices can be used. Lasersources, such as VCSELs, are mounted within the microprocessor forcommunicative optical coupling with the attached optical fibers. Thesubstrate in this example could be composed of plastic, ceramic, or anyother material suitable for securing and electrically couplingsemiconductor devices. An optional stabilizing strip 106 can be attachedacross the metal clad fibers, preferably near the top of the flexed cladfiber arch, made from a thermally conductive material which wouldprovide an additional heat dissipation path for heat traveling throughthe metal clad fibers and would also provide mechanical stabilizationfor the metal clad fibers.

Multiple fiber connectors 101 could be attached to the substrate forcoupling multiple ribbons of clad fibers to other ones of thesemiconductor devices. Additionally, the clad fiber ribbon as showncontains a plurality of clad fibers which could be coupled to severalsemiconductor chips mounted on the substrate.

FIG. 2 illustrates a detailed cross section of a prior art optical fiber202 having a metallic cladding 201. Various types of metal can be usedas cladding, although we have assumed copper in this preferredembodiment. Other materials that could be used include aluminum, gold,silver, among others. The metal provides a coating around a conventionalglass fiber (for example, a multimode fiber with a 50 micron glass coreand 125 micron metal cladding). Other commonly available glass cores orcladdings may have other dimensions, such as 62.5 micron optical fiber,however, the dimensions of the fiber and cladding are not an essentialaspect of the present invention. The microprocessor I/O is carried as anoptical signal in the glass fiber, while the metal outer cladding servesas a thermal conductor, and providing other advantages as outlinedabove, in this illustrated embodiment.

FIG. 3 illustrates a proposed design for the direct liquid jetimpingement (“DLJI”) cooling module 302. As shown in the figure, thismodule receives a cooling fluid via liquid supply opening 301 thendirects the cooling fluid directly onto an upper surface of amicroprocessor or other electronic device. The fluid is then directedacross the top surface of the electronic device, then to the sides ofthe device where it is returned through a liquid return path 303. Asealing frame 304 together with a sealing material secures the DLJImodule around the microprocessor chip or other semiconductor device.Preferred sealants include GE3280, a silicone adhesive produced byGeneral Electric, of Fairfield, Conn.; Sylgard 577 Silicone produced byDow Corning; or AbleBond 84-3, an electrically insulating epoxy chipadhesive; or AbleBond 7900 epoxy with sputtered metal coating, thelatter two produced by Ablestik Company of Rancho Dominguez, Calif.However, other sealants having a preferred property of providing a fluidtight seal can be used. A more detailed view of the seal frame assemblyis shown below, including the means to accommodate metal clad opticalfibers which act as extended surfaces for heat transfer to enhanceconvection cooling.

FIG. 4 illustrates a cross section of a portion of a DLJI module 405providing cooling fluid flow 403 over a top surface of an electronicdevice 404, which is typically mounted on a substrate though not shownas such in this figure. The fluid is ejected under pressure through aplurality of openings 402 in the bottom of an inlet plenum 401 of theDLJI module (shown as an orifice plate in FIG. 5). The pressure isprovided by flowing the cooling fluid through the inlet 301 and outthrough the outlet 303. By disposing the DLJI over the electronic devicethe pressurized cooling fluid will contact, and flow over, theelectronic device to carry away heat transferred from the electronicdevice to the cooling fluid. As illustrated more clearly in FIG. 6, theheat dissipation provided by the cooling fluid is enhanced through useof metal clad fibers. The cooling fluid flow over the metal clad fiberswill provide added heat dissipation due to the metal clad fibers beingthermally coupled to the heated semiconductor chip and thereby provideadditional thermal channels for heat to escape therefrom. Variouscooling fluids may be appropriate for use in the examples illustratedherein, such as water; dielectrics such as FC72—a fluorocarbonmanufactured by 3M; refrigerants such as R134A; or liquid metals such asmercury, gallium, and related alloys.

FIG. 5 illustrates an exploded view of the DLJI module showing inletfitting 501, DLJI manifold 502, orifice plate 503, fastening ring 504,fasteners 505, and sealing frame 506. A small notch at the bottom ofsealing frame 506 accommodates the metal clad fibers when the sealingframe is placed in position on the substrate surrounding themicroprocessor chip. The microprocessor module with optical I/O of FIG.1 is shown at 507 in relative position to the DLJI module apparatus.

FIG. 6 illustrates a cross section of a DLJI module attached to themicroprocessor module of FIG. 1. The inlet fitting 607 sits within theDLJI manifold 608 which sits within sealing frame 609 which further isseated within fastening ring 610. The expanded view illustrates orificeplate 601 above microprocessor die 606 which is sealed to the substrate604 and to sealing frame 602 by sealing material 607. The sealant shouldmake fluid tight contact at least with the semiconductor device 606 andthe sealing frame 602 such that cooling fluids used would not be able toreach the substrate surface. If the semiconductor device 606 includesmetallurgy on its bottom surface such that it is raised above the topsurface of the substrate then the sealant should be disposed at leastbetween the semiconductor device and the sealing frame, and optionallycontacting the substrate, so that cooling fluid does not leak intocontact with any such metallurgy. The clad fiber 603 is shown passingthrough sealing material 607. Also shown is a VCSEL 605 which is inoptical communication with the terminal end of metal clad fiber 603.

The general path of cooling fluid through the assembled apparatus ofFIG. 6 is as follows: cooling fluid enters the inlet fitting 607 throughthe inlet opening at the top and flows in a downward directionrepresented by the arrow 612. With respect to the expanded view, thecooling fluid passes over microprocessor 606 then flows away from themicroprocessor by passing over or, optionally, through metal clad fibers603, as represented by arrow 613, into a channel 611 that is coupled tothe outlet (303 of FIG. 3) for returning the cooling fluid.

With respect to the expanded view showing cooling fluid passing throughthe metal clad fiber 603, the metal clad fibers might optionally bestabilized by a jacket laminate that holds them together, as in aribbon, and in parallel. Hence, the cooling fluid might not be able topass through and underneath the metal clad fiber as in the presentpreferred embodiment illustrated in the expanded view of FIG. 6. In sucha case, the fluid might pass mostly over the top of the flexed metalclad fibers before being expelled from the DLJI module. Although thiswould provide an enhanced heat transfer cooling effect, it would not beas effective as the preferred embodiment wherein the cooling fluid flowsthrough and between the metal clad fibers.

Referring to FIG. 7, a thermally conductive epoxy, such as TIGA HTR-815silver filled epoxy from Resin Technology Group, LLC, of South Easton,Mass., or a solder 702 is used to assist in securing metal clad fiber703 to microprocessor die or other electronic device 701 and to providea thermally conductive path from the microprocessor die to the metalcladding. Heat generated by electric currents flowing in the wiringwithin die 701 increases the surface temperature of the die which thentransmits heat to the metal cladding via the epoxy or solder.Optionally, the metal clad fiber can be attached to the die without useof an epoxy or solder so long as the metal cladding is in direct contactwith the heated surface of the die so that a thermal pathway from thedie to the metal cladding is established.

While the preferred embodiment to the invention has been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

1. Apparatus comprising: a semiconductor chip; and a metal clad fiberoptically coupled to the semiconductor chip for transmitting data fromthe semiconductor chip and thermally coupled to the semiconductor chipfor conducting heat from the semiconductor chip.
 2. Apparatus of claim1, wherein a metal of the metal clad fiber is selected from the groupconsisting of aluminum, gold, copper, and silver.
 3. Apparatus of claim1 further comprising an epoxy for thermally coupling a metal of themetal clad fiber to the semiconductor chip.
 4. Apparatus of claim 1,further comprising: a DLJI module disposed over the semiconductor chipfor circulating cooling fluid over the semiconductor chip for contactingat least the metal clad fiber.
 5. Apparatus of claim 4, wherein the DLJImodule includes an inlet and an outlet for circulating substantially allof the cooling fluid.
 6. Apparatus of claim 5 further comprising a sealfor coupling the DLJI module around the semiconductor chip for providinga substantially fluid-tight fit.
 7. Apparatus of claim 4, wherein theDLJI module includes an inlet plenum disposed over the semiconductorchip and at least one ejection outlet for ejecting the cooling fluidonto the semiconductor chip and over the metal clad fibers.
 8. Apparatusof claim 6 wherein the seal is comprised of a flexible sealing materialdisposed between the DLJI module and at least a substrate upon which thesemiconductor chip is attached.
 9. Apparatus of claim 6 wherein the sealis comprised of an electrically insulating silicone adhesive material.10. Computer system comprising: a chip substrate for communicativelycoupling a plurality of semiconductor chips fastened thereon; and metalclad fibers physically and communicatively coupled to at least one ofsaid semiconductor chips for transmitting data to and from said at leastone of said semiconductor chips and for conducting heat away from saidat least one of said semiconductor chips.
 11. Computer system accordingto claim 10, further comprising: a DLJI module disposed over said atleast one of said semiconductor chips for circulating cooling fluid forcontacting at least the metal clad fibers.
 12. Computer system accordingto claim 11, wherein the DLJI module includes an inlet and an outlet forcirculating substantially all of the cooling fluid.
 13. Computer systemaccording to claim 11 further comprising a seal for coupling the DLJImodule around the semiconductor chip for providing a substantiallyfluid-tight fit.
 14. Computer system according to claim 10, wherein ametal of the metal clad fibers is selected from the group consisting ofaluminum, gold, copper, and silver.